The present invention relates to office chairs, and more particularly to tiltable office chairs that provide ergonomic seating positions for a user.
Conventional office chairs are configured to allow tilting of the seat and backrest in either an articulating manner or a synchronized tilt controlled manner. With articulating chair controls, or xe2x80x9cfixed-tiltxe2x80x9d controls, the seat and backrest tilt as a unit with the seat and backrest at all times remaining at a predetermined angle. With synchronized tilt, or xe2x80x9csynchro-tiltxe2x80x9d controls, the seat and backrest tilt, but at varying rates. For example, the backrest may tilt backward, or recline, at a rate twice the rate of the seat. Put another way, for every one degree the seat tilts, the backrest tilts two degrees. While synchro-tilt control chairs provide a more ergonomically correct tilting action, many municipalities, including the city of New York, require articulating control features so that the user may set the angle of the seat with respect to the backrest at a predetermined angle specific to the user. As a practical matter, a manufacturer is required to produce and inventory both the articulating and synchro-tilt chairs. Accordingly, given the typical lag time between production and sale, manufacturers may be stuck with an excessive supply of one type of chair and a deficiency of another, depending on consumers"" demand.
Articulating chair controls also allow the user to select the angle between the seat and back; however, after selection, that angle does not change when the chair tilts. With synchro-tilt controls, the relationship between the seat and backrest, as well as the rate of tilt of the seat with respect to the backrest, is predetermined by the design of the control. For example, in the upright position, the angle between the seat and backrest is fixed. As the seat and backrest tilt to a reclined position, the angle between the seat and backrest becomes larger than the angle between the seat and the backrest in the upright position, but the angle remains pre-determined by the design of the control. Thus, with both articulating and synchro-tilt controls, the angle between the seat and the backrest is limited to a single angular relation when the chair reclines or forward tilts.
Conventional office chairs are also provided with a forward tilt feature. This feature allows the user to either control the seat so that it does not tilt forward past the upright position, or, alternatively, control the seat to tilt forward past the upright position. In the forward tilt position, the pressure of the forward edge of the seat acting on the underside of a user""s leg is reduced while the feet of the user may remain flat on the floor in a comfortable stance. Conventional chairs come either with or without the forward tilt feature from the manufacturer. Accordingly, a distributor must produce and inventory chairs with and without the forward tilt feature. This can make ordering and inventory management difficult.
With conventional synchro-tilt control chairs, when the backrest and seat recline from the upright position, the angle between the seat and the backrest becomes larger. As noted above, the angle between the seat and the backrest increases at about a 2:1 ratio with respect to the angle of the seat to horizontal. Further, when the seat and backrest are tilted forward from the upright position, the angle between the seat and the back closes at the same 2:1 ratio. Accordingly, the user will typically find herself being xe2x80x9cclam-shelledxe2x80x9d between the seat and the backrest because the backrest is tilting forward at a rate greater than the forward tilting of the seat. This causes the user unnecessary discomfort and a potentially ergonomically incorrect position.
The aforementioned problems are overcome by the present invention wherein a chair tilt control is convertible between an articulating chair control and a synchro-tilt control, provides adjustment of the angle between a seat and backrest in synchro-tilt mode, is convertible between forward tilt and non-forward tilt; and provides a first rate of when the chair is reclined and a second rate when the chair is tilted forward.
In a first aspect of the invention, the chair control is convertible between an articulating, or xe2x80x9cfixed,xe2x80x9d tilt control or a synchro-tilt control. A chair manufacturer or distributor can convert the chair from one configuration to the other by simply configuring a lock mechanism in one of two positions. In the preferred embodiment, the control includes a housingxe2x80x94part of the chair basexe2x80x94which is pivotally attached to the seat. The backrest is pivotally attached to the seat. At a second pivot point on the backrest back lock mechanism, which is generally a mechanism of adjustable length, is attached to the backrest. One end of the bar is pivotally connected to the backrest. The other end of the bar may be attached to either a point on the seat or a point on the housing. If the bar is attached to the seat, the angle between the seat and the backrest does not change when the user reclines, thus attaining an articulating control. If the back lock bar is attached to the housing, the angle between the seat and back opens as the seat reclines, thus attaining a synchro-tilt control.
In a second aspect of the invention, the control enables the user to select the angle between the seat and the backrest even when the control is configured for synchro-tilt action. In the preferred embodiment, the adjustable synchro-tilt feature is incorporated into the above-described back lock mechanism. As noted above, the back lock is a bar of adjustable length. As a result of adjusting the length between the two points of connection of the back lock bar with the seat and the housing, the angle of the backrest changes in relation to the seat. Accordingly, a user may preselect the angular relationship between the seat and backrest of a synchro-tilt controlled chair as easily as a user may pre-select the angle in the articulating control chairs of the prior art.
In a third aspect of the invention, an office chair includes a forward tilt mechanism that may be enabled or disabled readily and easily, for example with the installation or removal of a lever. When the lever is removed, the forward tilt mechanism is disabled and the seat and backrest cannot tilt forward. When the lever is installed, a user may engage the forward tilt mechanism so that the seat and backrest tilt forward.
In a fourth aspect of the invention, the synchro-tilt chair control includes a dual-ratio action, meaning that the angle between the seat and back change at a first rate when the chair is reclined and at a second different rate when the chair is tilted forward. This feature solves the clam-shelling problem of the prior art. The geometry employed in the synchro-tilt control of the present invention is such that when the backrest and seat move from the neutral upright position into the forward tilt position, the rates of angular disposition of the backrest to the seat do not continue at the 2:1 ratio of the prior art. Rather, the closing movement reverses as the chair moves past the upright position so that the angle between the backrest and the seat increases. Accordingly, the backrest opens up with respect to the seat, therefore avoiding pinching of the user.